Routine clinical procedures for aromatic metabolite in body fluids are badly needed. We have developed an extremely sensitive technique for phenolic compounds which takes full advantage of both electrochemistry and high performance liquid chromatography to make selective measurement on the 10 pg level practical using a rather inexpensive apparatus. This approach forms the basis of clinical methods for catecholamines, metanephrines, homovanillic acid, vanillomandelic acid, dihydroxyphenylacetic acid, homogentisic acid, isoquinoline alkaloids, and related molecules in urine, blood, and cerbrospinal fluid. The assays are designed to maximize the clinically useful information obtainable by inexperienced personnel, while minimizing sample turnaround time. We are confident that data obtained by the new methods will be of higher quality than that presently available. The new assays will be used, with a large clinical population, to more completely evaluate the diagnostic and prognostic value of body fluid levels to tumors of the sympathetic nervous system, affective disorders, Parkinson's disease, acute myocardial infarction, alcoholism, essential hypertension, and muscular dystrophy. The combined efforts of analytical chemists, clinical chemists, medical technologists, and physicans during all phases of the program will insure that maximum benefit is derived from the resulting data. Besides tyrosine metabolism the methodology we have developed is well suited to studies of aromatic metabolism in general. Tryptophan metabolism is of special interest in that neurologically important information is available from serotonin, melatonin, and 5-hydroxyindole acetic acid (etc.) which can be correlated with catecholamine data.